This small grant application to the National Institute on Drug Abuse (NIDA) requests support for a secondary analysis of the economic impact of behavioral interventions currently implemented by the North Carolina Cooperative Agreement for AIDS Community-Based Outreach, Intervention, and Research (the NC CoOp study). The principal investigator, Dr. Anke Richter, requests these funds under the priority category of a new and less-experienced research investigator. The proposed effort will continue her dissertation work related to the economic assessment of interventions introduced to prevent the spread of HIV/AIDS in a high-risk population. Mathematical modeling provides a means of estimating epidemic progression and the ultimate outcomes of short-term behavioral interventions. Furthermore, the impact of future behavioral changes, such as possible relapses in HIV risk behavior after an intervention has been completed, can only be assessed via a model. Mathematical disease modeling permits us to link the observable short-term results with important long-term outcomes and permits important "what-if" analysis to assess the impact of small changes in disease or behavioral parameters. Combining a mathematical epidemic model that captures both the number of seroconversions and the time at which they occur with an economic model will enhance the economic analyses. The results will be more detailed and more accurate, thereby permitting a fuller comparison between intervention options. This proposal has three specific aims in performing an extensive economic impact analysis of the interventions implemented by the NC CoOp study: 1. Model the long-term effects (focusing on the number of HIV seroconversions and the time at which they occur) of the interventions implemented by the NC CoOp study on the urban, high- risk, primarily African-American, substance abusing community as a whole. 2. Identify the parameters (such as individual HIV risk behaviors) to which the mathematical epidemic and economic models are most sensitive and thereby identify targets for future policy and intervention programs for substance abusers. 3. Conduct a direct assessment of the cost/savings of the HIV interventions for substance abusers by incorporating a full epidemic model into the economic model.